The long term goal of the proposed experiments is to understand how animals perceive odors. The experiments in the present proposal are designed to improve our understanding of the function and role of the olfactory bulb in this process. Maps of the input to the bulb are available from optical recordings of calcium and pH signals. Here we propose to use optical recording methods to monitor the activity of postsynaptic cells in the olfactory bulb in an in vivo mouse preparation. First, we plan to use bulk injection of calcium dyes and 2-photon microscopy to simultaneously monitor the activity of many (hundreds) of individual neurons in response to odorant presentations. We plan to make these recordings from both juxtaglomerular neurons that surround the glomeruli and from mitral cells which provide the output of the olfactory bulb. The ability to record from many neurons simultaneously should greatly improve our understanding of olfactory bulb function. Second, we propose to use genetically encoded voltage-sensitive (FP-voltage sensor) or calcium- sensitive proteins expressed in the mitral/tufted cells to monitor the output of the bulb in response to odor presentations. A comparison of the output map with the input map would provide a strong statement about the function of the olfactory bulb in odorant processing. We propose modifications to improve the FP-voltage sensor signal-to-noise ratio and response time constant. These improvements would facilitate their use in any cell type in the mammalian brain and thereby contribute to the understanding of many aspects of brain function.RELEVANCE Olfactory function is compromised in a number of human diseases including Alzheimer's disease and Parkinson's disease (Schiffman, 1992; Doty, 2001). In Parkinson's disease and in the Thy1-aSyn mice mouse model of Parkinson's disease reduced odorant sensitivity is one of the earliest detected symptoms (Fleming and Chesselet, 2006). A hallmark of Parkinson's disease is the premature cell death of dopaminergic neurons; a substantial fraction of periglomerular neurons in the olfactory bulb are dopaminergic. Thus the experiments in the present proposal would not only further our basic understanding of olfactory processing but also allow a characterization of the neuronal substrate of the olfactory symptoms in mouse models. In addition, voltage sensitive dyes are regularly used to follow action potential propagation during cardiac arhythmias (e.g. Matiukas et al, 2006; Mironov et al, 2006). The heart is composed of a variety of cell types. Thus specific targeting of FP-voltage sensors would also be very useful in studying the causes treatment of arhythmias.